Piston and head damage

[Derekmj64]

I had a puzzling find on my snowmobile engine. Has anyone ever seen this on pistons? This is out of my 2017 Polaris 800 switchback assault engine (with 4,400 miles). I pulled the power valves out at the beginning of the week and noticed spherical dimples/craters on the tops of both pistons. It’s like someone put BBs in the cylinders (clutch side worse than the magneto side). I pulled the top end apart to find the clutch side piston has the dimples all the way around the perimeter and not anywhere else on the top of the piston and the Mag side had no where near as many, just isolated to one spot.

I have received feedback that the cause could be the main bearing coming apart and other people say detonation. The crank looks good from that I can see with the top end off, the rings are in good shape, wrist pin bearings are all intact and the ring locating pins are all there.

I am wondering if I caught a detonation issue before it got really bad? I’m scratching my head as to what could have caused this. I’ve never pulled pistons with this kind of damage.

I appreciate any input you may have.

 

[Polarisjackass]

I had a 2004XC 800 that I put a timing key in and cause something similar to that not quite as many so you may be right about the detonation

 

[Pro116]

It’s hard to tell by zooming in but that doesn’t look like detonation or melting. It looks like something was in your motor and made its way on top of the pistons. Are all the needles in the wrist pin bearings?

 

[Derekmj64]

All the needles are there. Probably going to tear the engine down the rest of the way this week. Someone suggested that it might be a ball bearing from the water pump but I thought I would have had a coolant issue if that was the case.

 

[Pro116]

Where all the circlips in when you move the wrist pins? I never had one of those motors apart so not sure what kind of pins there is in the bottom end but something had to come apart.

 

[Pro116]

Is the pins in the piston where the piston rings meet?

 

[Derekmj64]

All top end parts are in the correct locations and accounted for. Ring locating pins, the entire rings, wrist pin bearings....

 

[Snotwister]

So i have seen all your posts on other sires and it still looks like you never found anything. The only thing i can think of that might be possible is that i have seen where the small screws that hold the reeds to the reed block have come out before and caused that kind of damage. The head of the screw is about that size.

 

[Derekmj64]

I actually did figure it out and it was very unfortunate and 100% my fault. When I was cleaning the engine bay out I found small beads (still had no idea where these came from at this point). A couple days later I was messing with the hood on my bench and looked in windshield bag and found a silica packet that had broke open jammed in the very nose/front of the bag (I had no idea it was in there). The beads made it out of the bag and into the engine bay and intake. They were able to escape through small slit in the bag to allow for my 12V supply for charging my phone or GPS. If it wasn’t for bad luck, I’d have no luck at all.

 

[Snotwister]

Heading out to check my windshield bag now; lol. I just installed it the other day

 

[Derekmj64]

I would have been ok had I not cut a slit in the bottom of the bag to route a USB port.

 

[Derekmj64]

I am also going to seal up this part of the intake.

 

[Snotwister]

Silica bag was in my windshield bag also. Probably ok but better safe than sorry

 

[racer487]

At least you caught it before an explosion.

 

[Derekmj64]

At least you caught it before an explosion.

I agree and as bad as I feel about not preventing the cause, at least I found it so I’m not left wondering what happened.